Gas turbine diffuser with flow separator

ABSTRACT

A diffuser for use in a gas turbine engine, the diffuser having a first wall, a second wall, and a flow separator. The first and second wall define an annular cavity, with the annular cavity having an inlet. The first and second wall also forming a prediffuser that is proximate the inlet, and a dump region distal the inlet. The flow separator extends from the first wall into the annular cavity.

TECHNICAL FIELD

The present disclosure generally pertains to gas turbine engines, and ismore particularly directed toward a gas turbine diffuser.

BACKGROUND

Gas turbine engines include compressor, diffuser, combustor, and turbinesections. The diffuser reduces airflow velocity (conservation of mass)while increasing static pressure (Bernoulli's equation). The diffuseralso provides air to the combustor for the combustion reaction. Thediffuser assists in the proper control of the combustion process.

U.S. Pat. No. 7,984,614 issued to Nolcheff on Jul. 26, 2011 shows aplasma flow controlled diffuser system. In particular, the disclosure ofLin et al. is directed toward a diffuser system for a compressor for agas turbine engine including a diffuser and a plasma actuator. Thediffuser comprises a first wall and a second wall. The first and secondwalls form a diffuser flow passage there between. The plasma actuator isdisposed at least partially proximate the second wall. The plasmaactuator is adapted to generate an electric field to ionize a portion ofair flowing through the flow passage.

The present disclosure is directed toward overcoming known problemsand/or problems discovered by the inventors.

SUMMARY

A diffuser for use in a gas turbine engine, the diffuser having a firstwall, a second wall, and a flow separator. The first and second walldefine an annular cavity, with the annular cavity having an inlet. Thefirst and second wall also forming a prediffuser that is proximate theinlet, and a dump region distal the inlet. The flow separator extendsfrom the first wall into the annular cavity.

According to another embodiment, a method for retrofitting a diffuser ina gas turbine engine is also disclosed herein. The method includesremoving a preexisting diffuser from a gas turbine engine, andinstalling a diffuser having forced flow separation into the gas turbineengine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary gas turbine engine.

FIG. 2 is a cutaway side view of the diffuser from FIG. 1.

FIG. 3 is a schematic illustration superimposing both an uncut and cutstate of the diffuser of FIG. 2.

FIG. 4 is a flow chart of an exemplary method of retrofitting a diffuserin a gas turbine engine.

DETAILED DESCRIPTION

The systems and methods disclosed herein include a gas turbine enginediffuser with forced flow separation. In embodiments, the diffuser maybe configured to separate the flow of air from an interior wall duringoperation. The air is separated prior to entering a rapidly expanding“dump region”. Moreover, the diffuser may be configured such that theflow of air is forcibly and sufficiently separated to limit interactionat wall transitions, and to be subsequently be directed toward the feedof the injector.

FIG. 1 is a schematic illustration of an exemplary gas turbine engine.Some of the surfaces have been left out or exaggerated (here and inother figures) for clarity and ease of explanation. Also, the disclosuremay reference a forward and an aft direction. Generally, all referencesto “forward” and “aft” are associated with the flow direction of primaryair (i.e., air used in the combustion process), unless specifiedotherwise. For example, forward is “upstream” relative to primary airflow, and aft is “downstream” relative to primary air flow.

In addition, the disclosure may generally reference a center axis ofrotation of the gas turbine engine (“center axis” 95), which may begenerally defined by the longitudinal axis of its shaft 120 (supportedby a plurality of bearing assemblies 150). The center axis 95 may becommon to or shared with various other engine concentric components. Allreferences to radial, axial, and circumferential directions and measuresrefer to center axis 95, unless specified otherwise, and terms such as“inner” and “outer” generally indicate a lesser or greater radialdistance from, wherein a radial 96 may be in any direction perpendicularand radiating outward from center axis 95.

Structurally, a gas turbine engine 100 includes an inlet 110, a gasproducer or “compressor” 200, a diffuser 320, a combustor 300, a turbine400, an exhaust 500, and a power output coupling 600. One or more of therotating components are coupled by one or more shafts 120. Thecompressor 200 includes one or more compressor rotor assemblies 220. Thecombustor 300 includes one or more injectors 350 and includes one ormore combustion chambers 390. The turbine 400 includes one or moreturbine rotor assemblies 420. The exhaust 500 includes an exhaustdiffuser 520 and an exhaust collector 550.

As illustrated, the diffuser 320 is located downstream of the compressor200 and upstream of the combustor 300. According to one embodiment, thediffuser 320 mechanically interfaces between the compressor 200 and thecombustor 300. In alternate embodiments, diffuser 320 may be integratedwith the compressor 200, with the combustor 300, subdivided, or anycombination thereof.

Functionally, a gas (typically air 10) enters the inlet 110 as a“working fluid”, and is compressed by the compressor 200. In thecompressor 200, the working fluid is compressed in an annular flow path115 by the series of compressor rotor assemblies 220. In particular, theair 10 is compressed in numbered “stages”, the stages being associatedwith each compressor rotor assembly 220. For example, “4th stage air”may be associated with the 4th compressor rotor assembly 220 in thedownstream or “aft” direction—going from the inlet 110 towards theexhaust 500). Likewise, each turbine rotor assembly 420 may beassociated with a numbered stage. For example, first stage turbine rotorassembly 421 is the forward most of the turbine rotor assemblies 420.However, other numbering/naming conventions may also be used.

Once compressed air 10 leaves the compressor 200, it enters the diffuser320. The diffuser 320 is configured to diffuse the compressed air 10,and provide the air 10 to one or more injectors 350 and combustor linerin combustion chamber 390. Via the injector 350, air 10 and fuel 20 areinjected into the combustion chamber 390 and ignited. After thecombustion reaction, energy is then extracted from the combustedfuel/air mixture via the turbine 400 by each stage of the series ofturbine rotor assemblies 420. Exhaust gas 90 may then be diffused inexhaust diffuser 520 and collected, redirected, and exit the system viaan exhaust collector 550. Exhaust gas 90 may also be further processed(e.g., to reduce harmful emissions, and/or to recover heat from theexhaust gas 90).

One or more of the above components (or their subcomponents) may be madefrom stainless steel and/or durable, high temperature materials known as“superalloys”. A superalloy, or high-performance alloy, is an alloy thatexhibits excellent mechanical strength and creep resistance at hightemperatures, good surface stability, and corrosion and oxidationresistance. Superalloys may include materials such as HASTELLOY,INCONEL, WASPALOY, RENE alloys, HAYNES alloys, INCOLOY, MP98T, TMSalloys, and CMSX single crystal alloys.

FIG. 2 is a cutaway side view of the diffuser from FIG. 1. Inparticular, diffuser 320 is shown slightly rotated about its own centeraxis 329 such that a diffuser strut 325 located at TDC (top dead center)is out-of-cut. Note, the center axis 329 of the diffuser 320 may be thesame as the center axis 95 of the gas turbine engine, as illustratedhere. Additionally, for clarity and illustration purposes, certainfeatures/components have been added, removed, and/or simplified. Forexample, here, only one injector 350 is shown in the installed positionwithin diffuser 320, with other injector ports 344 shown vacant. Also,mating mounting interfaces are shown.

The diffuser 320 structurally includes members such as an outer housing321, an inner housing 322, a forward mounting interface 323, an aftmounting interface 324, and a plurality of diffuser struts 325. Theinner and outer housings 321, 322 form an annular cavity 326 having aninlet, and through which air 10 passes. The inner and outer housings321, 322 also form a prediffuser 330 and a dump region 340 discussedfurther below. The inner and outer housings 321, 322 may be singularstructures, assembled structures, or a combination thereof. For example,portions of the inner and outer housings 321, 322 may be divided and/orshared for ease of manufacture and/or assembly. According to oneembodiment, all or part of the inner and outer housings 321, 322 (aswell as other members) may be cast as a single unit.

The forward mounting interface 323 may be configured to attach thediffuser 320 to one or more upstream structures, such as to thecompressor 200. Similarly, the aft mounting interface 324 may beconfigured to attach the diffuser 320 to one or more downstreamstructures, such as to the combustor case 310. According to oneembodiment, the forward mounting interface 323 and the aft mountinginterface 324 may include circumferential flanges radiating radiallyaway from the annular cavity 326, which then mount to mating interfacesusing conventional means, such as a circumferential array of fasteners.

The plurality of diffuser struts 325 radially extend between at least aportion of the outer housing 321 and at least a portion of the innerhousing 322, and are radially distributed around the annular cavity 326.The plurality of diffuser struts 325 support inner and outer housings321, 322 relative to each other, and may include one or more radialpassageways within each strut 325 configured to provide access toportions of the diffuser 320 that are radially inward of the innerhousing 322. Accordingly, the one or more radial passageways (not shown)within each strut 325 provide a protected passage through the annularcavity 326. Although only two struts 325 are illustrated here, accordingto one embodiment, diffuser 320 may include seven struts 325.

The diffuser 320 functionally is a divergent duct, including both aprediffuser 330 and a dump region 340. The prediffuser 330 may be formedby upstream portions of the inner and outer housings 321, 322.Similarly, the dump region 340 may be formed by downstream portions ofthe inner and outer housings 321, 322. According to one embodiment, atleast a portion of the prediffuser 330 may be formed by anothercomponent, such as the compressor 200. According to another embodiment,at least a portion of the dump region 340 may be formed by anothercomponent, such as an inner bearing housing or combustor 300.

The prediffuser 330 includes a prediffuser inlet 331, a prediffuser exit332, and a prediffuser flowpath 333 there between. The prediffuser inlet331 is the portion of the prediffuser 330 that first receives air 10from the compressor 200, which may also serve as the diffuser inlet. Theprediffuser exit 332 is the portion of the prediffuser 330 where air 10leaves the prediffuser 330. The prediffuser flowpath 333 is the portionof the annular cavity 326 that is within the prediffuser 330.

Additionally, the prediffuser 330 includes a prediffuser outer wall 334and a prediffuser inner wall 335. The prediffuser outer wall 334 may beformed by an inner surface of the outer housing 321. Similarly, theprediffuser inner wall 335 may be formed by an outer surface of theinner housing 322.

The prediffuser 330 is configured to diffuse compressed, high velocityair 10 exiting the compressor 200 in a stable and controlled manner.Aerodynamic considerations that may be important in the configuration ofthe prediffuser 330 may include a short flow path, a uniform flowdistribution, and low drag loss. According to one embodiment, theprediffuser outer wall 334 and the prediffuser inner wall 335 mayinclude machined finishes on surfaces exposed to air 10 (i.e., withinthe prediffuser flowpath 333).

According to another embodiment, the prediffuser 330 may expand on onlyone wall. In particular, one wall may run parallel with air while theother wall expands away from the first wall. For example, theprediffuser inner wall 335 may extend from the compressor, substantiallyparallel with the flow direction of air 10 in the prediffuser flowpath333 at the prediffuser inlet 331. Meanwhile, the prediffuser outer wall334 may form a frustum (i.e., a truncated cone with a linearly expandingradius) between the prediffuser inlet 331 and the prediffuser exit 332.Additionally, the outer may begin parallel with the prediffuser innerwall 335 for a transition distance, before expanding. In otherembodiments, the prediffuser outer wall 334 may include a non-linearcurvature along its axis. Similarly, the prediffuser inner wall 335 mayinclude non-linear curvature along its axis. Moreover, the prediffuserinner wall 334 and outer wall 335 may both expand in radius with theonly constraint being exit cross-sectional area is greater than inletcross-sectional area.

The dump region 340 includes a dump region outer wall 341, a dump regioninner wall 342, and an expansion cavity 343. Like in the prediffuser330, the dump region outer wall 341 may be formed by an inner surface ofthe outer housing 321, and the dump region inner wall 342 may be formedby an outer surface of the inner housing 322.

The expansion cavity 343 is formed by the dump region outer wall 341 andthe dump region inner wall 342, and intersected by the plurality ofdiffuser struts 325. The expansion cavity 343 is a portion of theannular cavity 326 rapidly expands once sufficient kinetic energy isrecovered via the prediffuser 330. Compared to the prediffuser 330, thedump region 340 is less sensitive to aerodynamic considerations. Forexample, according to one embodiment, one or both of the dump regionouter wall 341 and the dump region inner wall 342 may retain castsurfaces within the expansion cavity 343.

The diffuser 320 also includes a prediffuser-dump region interface 327and a flow separator 328. The flow separator 328 is located proximate,but upstream from the prediffuser-dump region interface 327 and will bediscussed further below. The prediffuser-dump region interface 327 islocated between the prediffuser 330 and the dump region 340. Inparticular, the prediffuser-dump region interface 327 is the part of thediffuser 320 where the prediffuser 330 and the dump region 340 meet. Theprediffuser-dump region interface 327 may include edges and/ordiscontinuities on both the outer housing 321 and the inner housing 322.In particular, the edges or discontinuities are located at the unions ofthe prediffuser outer wall 334 and the dump region outer wall 341,and/or at the prediffuser inner wall 335 and dump region inner wall 342,respectively.

As the diffuser 320 may be cast as a single unit, the prediffuser-dumpregion interface 327 may be identified by a transition in the outerhousing 321 (and/or the inner housing 322) from a machine finish to acast finish. Alternately, the prediffuser-dump region interface 327 maybe identified by a substantial discontinuity in the rate of expansion ofthe annular cavity 326. The prediffuser exit 332 is the portion of theannular cavity 326 corresponding to the prediffuser-dump regioninterface 327.

The flow separator 328 is a member extending from prediffuser 330. Theflow separator 328 is configured to cause airflow separation from atleast one of the prediffuser outer wall 334 and the prediffuser innerwall 335. Additionally, the flow separator 328 may be configured toprevent the flow of air 10 from shifting during engine operation. Inparticular, the flow separator 328 extends into the prediffuser flowpath333 from at least one of the prediffuser outer wall 334 and theprediffuser inner wall 335. According to one embodiment, the flowseparator 328 may extend normally from the surface in which it is fixed,i.e., perpendicular to an angle of diffusion/expansion. Alternately, theflow separator 328 may extend normal to the center axis of the diffuser320.

The flow separator 328 may be fixed to the prediffuser 330, and made ofthe same or a similar material as the prediffuser 330. In particular,the flow separator 328 may be integrated into the prediffuser 330, ormay be added to and secured onto the prediffuser 330. For example, wherethe flow separator 328 is integrated into the prediffuser 330, it may becast as a feature of the diffuser 320. As a cast feature, it may besubject to certain post-casting machine work, or finishing. Also forexample, where the flow separator 328 is added and secured onto theprediffuser 330, it may be made from the same or similar material as theprediffuser 330 and joined to the prediffuser 330 through brazing orwelding. As add-on member, the prediffuser 330 may first be subject topre-joining machine work, or finishing to better receive the flowseparator 328.

According to one embodiment, flow separator 328 may be made after aninitial casting. In particular, the flow separator 328 may be added tothe prediffuser 330. For example, once the diffuser 320 has been castand finished, a receiving notch 337 may cut into the desired wall (here,the prediffuser outer wall 334) and the flow separator 328 may beinserted in the notch. Any convenient shape may be used for thereceiving notch 337. For example here the receiving notch 337 has arectangular shape matching that of a received end of the flow separator328. Once the flow separator 328 is received in the receiving notch 337it may be joined using conventional methods such as brazing or welding.

With this embodiment, a preexisting diffuser may be retrofit into thediffuser 320, having the flow separator 328. In particular, apreexisting diffuser may be machined to include a receiving notch 337,and a flow separator 328 may be added and joined. For example, asillustrated and as with a new manufacture, a prediffuser outer wall 334of the preexisting diffuser may have receiving notch 337 machined intoit. Then flow separator 328 may be inserted into the receiving notch337. According to one embodiment, the flow separator 328 may be brokeninto two or more segments to facilitate installation. Additionally,according to one embodiment, the flow separator 328 may be press fitinto the receiving notch 337.

FIG. 3 is a schematic illustration superimposing both an uncut and cutstate of the diffuser of FIG. 2. In particular, the dark line representsthe diffuser 320 after casting but before machine finishing isperformed. This is to illustrate cutting the flow separator 328 directlyout of the casting. As discussed above, there are multiple methods tomake the flow separator 328, including but not limited to integrating itinto the prediffuser 330 as part of a casting, or subsequently addingand secured it onto the prediffuser 330. Accordingly, FIG. 3 illustratesthe former approach to making the flow separator 328. Note, in thisembodiment the diffuser 320 is cast without the prediffuser inner wall335 (FIG. 2).

Flow separator 328 may be made as part of an initial casting. Inparticular, the diffuser 320 may be cast with additional material instrategic locations to subsequently be machined off and form the flowseparator 328. For example, in this embodiment, the diffuser 320 mayinclude an excess cast layer 336 in the region of the prediffuser outerwall 334, as well as other surfaces to be machined. The excess castlayer 336 is illustrated by a darker line in the figure. The excess castlayer 336 is material cast in addition to any material to needed tofinish the surface of the prediffuser outer wall 334. According to oneembodiment the excess cast layer 336 includes sufficient excess castingmaterial to machine the flow separator 328 into the diffuser 320 whilein a cast or rough machined state. According to another embodiment theexcess cast layer 336 is at least the thickness of the height 345 of theflow separator 328.

With the addition of the excess cast layer 336 the flow separator 328may be directly integrated into the diffuser 320. In particular, theflow separator 328 may be formed by cutting away excess material of theexcess cast layer 336. According to one embodiment, the flow separator328 may be formed as part of a finish operation of the prediffuser outerwall 334. According to another embodiment, the flow separator 328 may beformed prior to a finish operation of the prediffuser outer wall 334.According to another embodiment, the flow separator 328 may be formed aspart of a separate machining operation after a finish operation of theprediffuser outer wall 334.

The flow separator 328 forms an irregularity in the prediffuser flowpath333. In particular, the flow separator 328 includes a profile thatinterrupts airflow around the annular cavity 326 near or at theprediffuser exit 332 during operation of the gas turbine engine.According to one embodiment the flow separator 328 may have a generallyrectangular profile. In particular, when viewed radially as illustrated(side view), the flow separator 328 may include a height 345 and a width346 in its profile, with the corresponding exposed (i.e., to air 10during operation) surfaces joined at or about right angles.

In addition, the flow separator 328 may form a continuous, uninterruptedbarrier. According to one embodiment, the flow separator 328 may includea member that circumscribes one or both of the prediffuser outer wall334 and the prediffuser inner wall 335 (FIG. 2) and extends into theprediffuser flowpath 333. According to one embodiment, the circumscribedflow separator 328 may be angled such that it defines a plane or planarregion, which is normal to the center axis 329 of the diffuser.

According to one embodiment the flow separator 328 may be configured tocause separation while minimizing losses. In particular, the flowseparator 328 may be short, narrow, and have a sharp edge. For example,the flow separator 328 may have a short height, the height 345 onlyextending into the prediffuser flowpath 333 by ten percent, by less thanten percent, or between five and fifteen percent of the radial distancebetween the prediffuser outer wall 334 and the prediffuser inner wall335 (FIG. 2). Alternately, the flow separator 328 may have a height 345of 0.18″, 0.1875″ or less, or between 0.09″ and 0.27″. Also for example,the flow separator 328 may have a thickness or width 346, measuring inthe axial direction, of 0.125″ or less, or between 0.0625″ and 0.25″.Also for example, the flow separator 328 may have a sharp edge generallyforming a right angle, with a generally rectangular profile (asdescribed above) and/or having a thickness-to-height ratio of 0.7, lessthan 0.7, or between 0.6-0.8. Alternately, the flow separator 328 mayhave a sharp corner on its upstream face to induce clean flowseparation, for example, the flow separator 328 may have a “break edge”requirement or leading corner radius <0.030″.

According to one embodiment, the flow separator 328 may extend from onlyone of the prediffuser outer wall 334 and the prediffuser inner wall 335(FIG. 2). In particular, where only one wall draws away from the flow ofthe air 10, the flow separator 328 may circumscribe only one of theprediffuser outer wall 334 and the prediffuser inner wall 335.Alternately, the flow separator 328 may extend from the wall having thehighest velocity profile. Similarly, where one wall expands theprediffuser flowpath 333 at a greater rate than the other wall, the flowseparator 328 may extend from that wall. For example, as illustratedhere, the prediffuser inner wall 335 is substantially parallel with theflow direction of air 10, and the prediffuser outer wall 334 linearlyexpands between the prediffuser inlet 331 and the prediffuser exit 332(with the exception of a transition region 338 proximate the prediffuserinlet 331). Thus, in this case the flow separator 328 may extend fromthe prediffuser outer wall 334.

According to one embodiment, the flow separator 328 may be locatedproximate the prediffuser-dump region interface 327. In particular, theflow separator 328 may be located at the prediffuser-dump regioninterface 327 or in the prediffuser 330 immediately upstream of theprediffuser-dump region interface 327.

For example, the flow separator 328 may be located at a distance of 1times the width 346, less than 3 times the width 346, or between 0.5times the width 346 and 4.5 times the width 346. Alternately, the flowseparator 328 may be located at a distance from the prediffuser-dumpregion interface 327 selected such that, under normal operatingconditions, the air 10 is prevented from attaching to the dump regionouter wall 341 or the dump region inner wall 342. In addition, the flowseparator 328 may be located at a distance from the prediffuser-dumpregion interface 327 selected such that, the air 10 is prevented fromattaching to the dump region outer wall 341 or the dump region innerwall 342 under transient operating conditions.

INDUSTRIAL APPLICABILITY

Gas turbine engines, including stationary and motive gas turbineengines, and thus their components, may be suited for any number ofindustrial applications, such as, but not limited to, various aspects ofthe oil and natural gas industry (including include transmission,gathering, storage, withdrawal, and lifting of oil and natural gas),power generation industry, cogeneration, aerospace and transportationindustry, to name a few examples.

Generally, embodiments of the presently disclosed gas turbine diffuserare applicable to the use, operation, maintenance, repair, andimprovement of gas turbine engines, and may be used in order to improveperformance and efficiency, decrease maintenance and repair, and/orlower costs. In addition, embodiments of the presently disclosed gasturbine diffuser may be applicable at any stage of the gas turbineengine's life, from design to prototyping and first manufacture, andonward to end of life. Accordingly, the gas turbine diffuser may be usedin a first product, as a retrofit or enhancement to existing gas turbineengine, as a preventative measure, or even in response to an event. Thisis particularly true as the presently disclosed gas turbine diffuser mayconveniently include identical interfaces to be interchangeable with apreexisting type of gas turbine diffuser.

FIG. 4 is a flow chart of an exemplary method of retrofitting a diffuserin a gas turbine engine. In particular, the method corresponds toretrofitting the gas turbine engine with a diffuser 320 having forcedflow separation. The method generally includes the steps of removing apreexisting diffuser from a gas turbine engine 952, and installing adiffuser having forced flow separation into the gas turbine engine 966.

The method may further include manufacturing the diffuser 954 orreconditioning the diffuser 960. As discussed in greater detail above,manufacturing the diffuser 954 may include casting the diffuserincluding an excess cast layer 956 and machining the flow separator intothe casting 958. Alternately, the diffuser 954 may include machining areceiving notch into the diffuser 962 and installing a flow separatorinto the diffuser 964. Similarly, reconditioning the diffuser 960 mayinclude machining a receiving notch into the diffuser 962 and installinga flow separator into the diffuser 964.

Once compressed air 10 leaves the compressor 200, it enters the diffuser320. In the prediffuser 330 compressed, high velocity air 10 exiting thecompressor 200 is diffused in a stable and controlled manner and then“dumped” in the dump region 340. The diffuser 320 is configured todiffuse the compressed air 10, and provide the air 10 to one or moreinjectors 350.

The one or more injectors 350 may be axially fed the diffused air 10. Inparticular, the one or more injectors 350 may have an axial feedarrangement of the swirler, where the feed of the airflow is directlyinto the dome of the injector 350. For example and as illustrated, theone or more injectors 350 may be “L shaped” lean premix axial flowinjectors. Where the velocity profile of the air 10 entering the one ormore injectors 350 varies sufficiently, engine performance and oremissions may be affected. Transient conditions however, are difficultto identify, let alone treat.

The inventor has discovered through extensive testing that the air 10may attach to or otherwise be influenced by an expanding wall of thedump region 340 (here, the dump region outer wall 341) as it passes theprediffuser exit 332. In particular, flowpath variations andimperfections can lead to flowfield instabilities, separation zones andinconsistencies. Leakages downstream of the prediffuser 330 may also beinfluencing flow behavior. In addition, the flowfield may take ondifferent “character” after load swing or shutdown/restart scenario. Forexample the boundary layer state may not be predictable (i.e., sometimes“attached” and sometimes not). Sufficient variation of the airflow mayalso affect NOx in the combustion process.

By separating the flow of air 10 from the expanding wall, prior to theprediffuser-dump region interface 327, greater resistance to transientconditions such as flow fluctuations induced by the dump region 340 maybe achieved. In particular, the flow of air 10 may be separated so as tobe directed toward the feed of the injector 350. Moreover, the flowseparator 328 forcing flow to cleanly separate from the prediffuser 330in a predictable and repeatable manner with the sharp edge or “tripstrip” may mitigate any interaction the prediffuser 330 and the dumpregion 340 in the first instance.

The preceding detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. The described embodiments are not limited to use inconjunction with a particular type of gas turbine engine. Hence,although the present embodiments are, for convenience of explanation,depicted and described as being implemented in a stationary gas turbineengine, it will be appreciated that it can be implemented in variousother types of gas turbine engines, and in various other systems andenvironments. Furthermore, there is no intention to be bound by anytheory presented in any preceding section. It is also understood thatthe illustrations may include exaggerated dimensions and graphicalrepresentation to better illustrate the referenced items shown, and arenot consider limiting unless expressly stated as such.

What is claimed is:
 1. A diffuser for use in a gas turbine engine, thediffuser comprising: a first prediffuser wall; a second prediffuserwall, the first prediffuser wall and the second prediffuser walldefining an annular cavity having an inlet and an outlet and defining anannular prediffuser airflow path from the inlet to the outlet, the firstprediffuser wall and the second prediffuser wall diverging from theinlet to the outlet forming a prediffuser, the first prediffuser walldiverging in a downstream direction at a first angle relative to adiffuser center axis; a dump region having a first dump region wall anda second dump region wall; the first dump region wall extending from thefirst prediffuser wall at the outlet; the first dump region wall and thesecond dump region wall defining an expansion cavity, the first dumpregion wall and the second dump region wall diverging as the expansioncavity extends from the outlet, the first dump region wall diverging inthe downstream direction at a second angle relative to the diffusercenter axis, wherein the second angle is greater than the first angle; aflow separator extending radially from the first prediffuser wall intothe annular cavity proximate and upstream of the outlet, the flowseparator having a rectangular profile and extending into the annularprediffuser airflow path through the annular cavity to form a barrierfacing the inlet which opposes an airflow along the first prediffuserwall, the flow separator is configured to separate the airflow from thefirst prediffuser wall before the airflow enters the dump region therebycreating a separated airflow, wherein neither the dump region nor theprediffuser include a vortex chamber or a bleed air port, locatedadjacent to the flow separator, used to influence the separated airflowadjacent to the barrier; and wherein the diffuser is configured forattachment to an upstream end of a combustor of the gas turbine engine.2. The diffuser of claim 1, wherein the flow separator includes a heightand a width; and wherein a ratio of the width to the height is between0.6-0.8.
 3. The diffuser of claim 1, further comprising aprediffuser-dump region interface between the prediffuser and the dumpregion; and wherein the flow separator is located proximate theprediffuser-dump region interface.
 4. The diffuser of claim 1, whereinthe flow separator is integrated into the prediffuser as part of acasting of the prediffuser.
 5. The diffuser of claim 1, wherein the flowseparator includes a height and a width; and wherein the height of theflow separator is between five and fifteen percent of a distance betweenthe first prediffuser wall and the second prediffuser wall.
 6. Thediffuser of claim 5, wherein the width of the flow separator is between0.0625″ and 0.25″.
 7. The diffuser of claim 6, wherein the height of theflow separator is between 0.09″ and 0.27″; and wherein the flowseparator circumscribes at least one of the first prediffuser wall andthe second prediffuser wall.
 8. A combustor for use in a gas turbineengine, the combustor including the diffuser of claim
 1. 9. A gasturbine engine including the diffuser of claim 1, wherein the gasturbine engine includes a compressor and a turbine; and wherein thediffuser is located downstream of the compressor and upstream of theturbine.
 10. A diffuser for use in a gas turbine engine, the diffusercomprising: a dump region including a dump region outer wall and a dumpregion inner wall defining an expansion cavity; a prediffuser disposedupstream of the dump region, the prediffuser including a prediffuserouter wall and a prediffuser inner wall forming an annular airflow pathwith an inlet and an outlet, the prediffuser expanding from the inlet tothe outlet, the prediffuser outer wall diverging in a downstreamdirection at a first angle relative to a diffuser center axis; the dumpregion outer wall extending from the prediffuser outer wall at theoutlet and diverging in the downstream direction at a second anglerelative to the diffuser center axis, wherein the second angle isgreater than the first angle; a flow separator extending radially inwardfrom the prediffuser outer wall into the annular airflow path and towardthe prediffuser inner wall proximate and upstream of the dump region,the flow separator having a rectangular profile forming a barrier facingthe inlet which opposes an airflow along the prediffuser outer wall andis configured to separate the airflow from the prediffuser outer wallbefore the airflow enters the dump region thereby creating a separatedairflow, the flow separator is configured to direct the separatedairflow towards the prediffuser outlet, wherein neither the dump regionnor the prediffuser include either of: a vortex chamber or a bleed airport, located adjacent to the flow separator, used to influence theseparated airflow adjacent to the barrier; and wherein the diffuser isconfigured for attachment to an upstream end of a combustor of the gasturbine engine.
 11. The diffuser of claim 10, wherein the flow separatorincludes a height and a width; and wherein the flow separator is locatedupstream of the dump region by a distance less than 3 times the width ofthe flow separator.
 12. The diffuser of claim 10, wherein the flowseparator includes a height and a width; and wherein the flow separatoris located upstream of the dump region by a distance between 0.5 timesthe width and 4.5 times the width of the flow separator.
 13. A diffuserfor use in a gas turbine engine, the diffuser comprising: an outerhousing including a prediffuser outer wall, and a dump region outer wallextending from the prediffuser outer wall; an inner housing locatedwithin the outer housing, the inner housing including a prediffuserinner wall located inward from the prediffuser outer wall, theprediffuser inner wall and the prediffuser outer wall forming aprediffuser that includes an inlet and an outlet and defines an annularprediffuser airflow path from the inlet to the outlet, the prediffuserexpanding from the inlet to the outlet, the prediffuser outer walldiverging in a downstream direction at a first angle relative to adiffuser center axis, and a dump region inner wall located inward fromthe dump region outer wall, the dump region inner wall and the dumpregion outer wall defining a dump region forming an expansion cavityextending from the prediffuser outlet, the dump region outer walldiverging in the downstream direction at a second angle relative to thediffuser center axis, wherein the second angle is greater than the firstangle; and a flow separator extending radially into the annularprediffuser airflow path from the prediffuser outer wall towards theprediffuser inner wall, the flow separator being adjacent to andupstream of the dump region outer wall; and the flow separator having arectangular profile forming a barrier which faces the inlet and opposesan airflow along the prediffuser outer wall and is configured toseparate the airflow from the prediffuser outer wall thereby creating aseparated airflow, the flow separator is configured to direct theseparated airflow into the annular prediffuser airflow path prior to theseparated airflow entering the dump region, wherein neither the dumpregion nor the prediffuser include either of: a vortex chamber or ableed air port, located adjacent to the flow separator, used toinfluence the separated airflow adjacent to the barrier; and wherein thediffuser forms a portion of a combustor of the gas turbine engine. 14.The diffuser of claim 13, wherein the prediffuser outer wall forms afrustum between the inlet and the outlet, and wherein the prediffuserouter wall expands from the inlet to the outlet.
 15. The diffuser ofclaim 13, wherein the prediffuser outer wall and the prediffuser innerwall include a machined finish, and wherein the dump region outer walland the dump region inner wall include a cast finish.
 16. The diffuserof claim 15, further comprising a prediffuser-dump region interfacelocated at the outlet, wherein the outer housing transitions from themachined finish to the cast finish.
 17. The diffuser of claim 13,wherein the outer housing includes a discontinuity in a rate ofexpansion between the prediffuser outer wall and the dump region outerwall.